Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$44.84	7.380%	$48.1492	$48.15	$48.15	$48.10
Purchase #2	$199.86	11.648%	$223.1397	$223.14	$223.15	$223.10
Purchase #3	$139.29	4.752%	$145.9091	$145.91	$145.90	$145.90
Purchase #4	$204.48	3.399%	$211.4303	$211.43	$211.45	$211.40
Purchase #5	$169.87	6.268%	$180.5175	$180.52	$180.50	$180.50
Purchase #6	$233.88	7.547%	$251.5309	$251.53	$251.55	$251.50
Purchase #7	$116.61	10.175%	$128.4751	$128.48	$128.50	$128.50
7 purchase totals =	$1,108.83		$1,189.1518	$1,189.16	$1,189.20	$1,189.00